Year	%
1980	10.2
1986	9.8
1987	9.2
1991	9.1
1992	9.2
1993	9.3
1994	9
1995	8.4
1996	8.2
1997	8.2
1998	7.8
1999	8
2000	7.6
2001	7.1
2002	6.9
2003	7.5
2004	8.1
2005	8.3
2006	8.7
2007	8.6
2008	9
2009	9.3
2010	9.2
2011	9.6
2012	9.9
2013	10
2014	9.7
2016	9.7
2017	10